can: rockchip_canfd: prepare to use full TX-FIFO depth

So far the TX-FIFO is only used with a depth of 1, although the
hardware offers a depth of 2.

The workaround for the chips that are affected by erratum 6, i.e. EFF
frames may be send as standard frames, is to re-send the EFF frame.
This means the driver cannot queue the next frame for sending, as long
ad the EFF frame has not been successfully send out.

Introduce rkcanfd_get_effective_tx_free() that returns "0" space in
the TX-FIFO if an EFF frame is pending and the actual free space in
the TX-FIFO otherwise. Then replace rkcanfd_get_tx_free() with
rkcanfd_get_effective_tx_free() everywhere.
Tested-by: Alibek Omarov <a1ba.omarov@gmail.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20240904-rockchip-canfd-v5-16-8ae22bcb27cc@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/rockchip/rockchip_canfd-rx.c

@@ -124,7 +124,7 @@ static int rkcanfd_rxstx_filter(struct rkcanfd_priv *priv,
 
 		WRITE_ONCE(priv->tx_tail, priv->tx_tail + 1);
 		netif_subqueue_completed_wake(priv->ndev, 0, 1, frame_len,
-					      rkcanfd_get_tx_free(priv),
+					      rkcanfd_get_effective_tx_free(priv),
 					      RKCANFD_TX_START_THRESHOLD);
 
 		*tx_done = true;

drivers/net/can/rockchip/rockchip_canfd-tx.c

@@ -8,6 +8,40 @@
 
 #include "rockchip_canfd.h"
 
+static bool rkcanfd_tx_tail_is_eff(const struct rkcanfd_priv *priv)
+{
+	const struct canfd_frame *cfd;
+	const struct sk_buff *skb;
+	unsigned int tx_tail;
+
+	if (!rkcanfd_get_tx_pending(priv))
+		return false;
+
+	tx_tail = rkcanfd_get_tx_tail(priv);
+	skb = priv->can.echo_skb[tx_tail];
+	if (!skb) {
+		netdev_err(priv->ndev,
+			   "%s: echo_skb[%u]=NULL tx_head=0x%08x tx_tail=0x%08x\n",
+			   __func__, tx_tail,
+			   priv->tx_head, priv->tx_tail);
+
+		return false;
+	}
+
+	cfd = (struct canfd_frame *)skb->data;
+
+	return cfd->can_id & CAN_EFF_FLAG;
+}
+
+unsigned int rkcanfd_get_effective_tx_free(const struct rkcanfd_priv *priv)
+{
+	if (priv->devtype_data.quirks & RKCANFD_QUIRK_RK3568_ERRATUM_6 &&
+	    rkcanfd_tx_tail_is_eff(priv))
+		return 0;
+
+	return rkcanfd_get_tx_free(priv);
+}
+
 static void rkcanfd_start_xmit_write_cmd(const struct rkcanfd_priv *priv,
 					 const u32 reg_cmd)
 {
@@ -42,7 +76,7 @@ int rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 		return NETDEV_TX_OK;
 
 	if (!netif_subqueue_maybe_stop(priv->ndev, 0,
-				       rkcanfd_get_tx_free(priv),
+				       rkcanfd_get_effective_tx_free(priv),
 				       RKCANFD_TX_STOP_THRESHOLD,
 				       RKCANFD_TX_START_THRESHOLD)) {
 		if (net_ratelimit())
@@ -99,7 +133,7 @@ int rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	rkcanfd_start_xmit_write_cmd(priv, reg_cmd);
 
 	netif_subqueue_maybe_stop(priv->ndev, 0,
-				  rkcanfd_get_tx_free(priv),
+				  rkcanfd_get_effective_tx_free(priv),
 				  RKCANFD_TX_STOP_THRESHOLD,
 				  RKCANFD_TX_START_THRESHOLD);
 

drivers/net/can/rockchip/rockchip_canfd.h

@@ -533,6 +533,7 @@ int rkcanfd_handle_rx_int(struct rkcanfd_priv *priv);
 
 void rkcanfd_timestamp_init(struct rkcanfd_priv *priv);
 
+unsigned int rkcanfd_get_effective_tx_free(const struct rkcanfd_priv *priv);
 void rkcanfd_xmit_retry(struct rkcanfd_priv *priv);
 int rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev);
 void rkcanfd_handle_tx_done_one(struct rkcanfd_priv *priv, const u32 ts,